Confused and worried help please!!!

Cynthia

I am 18 weeks 3 days pregnant and today my doctor told me that they had to do my anatomy scan again even though he says everything is good on the first one. He also told me that if I wanted to get a chromosomal test and gender blood test. I really though this was done between the week of 13 and 15. I am so confused and worried something is wrong with my baby.